1. Field of the Invention and Contract Statement
The invention relates to direct current plasma emission spectrometers for use in combination with microcolumn liquid and gas chromatographs.
2. Discussion of Background and Prior Art
Chromatography is a physical method of separation, in which the components to be separated are distributed between two phases; one of these phases constituting a stationary bed of large surface area, and the other being a fluid that percolates through or along the stationary bed. The stationary phase can be either a solid or a liquid, and the moving phase may be either a liquid or a gas. All of the known types of chromatography broadly fall into four categories, namely liquid-solid, gas-solid, liquid-liquid, and gas-liquid. In all of the known chromatographic techniques, the solutes to be separated migrate along a column (or, as in paper or thin layer chromatography, the physical equivalent of a column), and of course the basis of the separation lies in different rates of migrations for the different solutes. The rate of migration of a solute is the result of two factors, one tending to move the solute and the other to retard it.
Liquid chromatography (LC) is a rapidly expanding analytical technique for the separation of chemical compounds which have low or non-existent vapor pressures and are water soluble. The conventional detection systems for liquid chromatography are based on the refractive indices, absorption, fluorescent or electrochemical properties of the compounds in question. Such detectors do not offer selectively or sensitivity of the magnitude provided by detectors for gas chromatograpy.
Micro-column liquid chromatographic systems are currently in the infancy of the state-of-the-art development of liquid chromatography. Three basic nomenclatures define micro-column liquid chromatography: (1) open tubular liquid chromatography; (2) microbore liquid chromatography; and (3) capillary liquid chromatography. Inherent with all three designs are (a) extremely high theoretical plate separations, (b) high mass sensitivities and (c) extremely low solvent flow rates (1 to 5 ml/min. as compared to 40 to 100 ml/min. for conventional liquid chromatographs).
In plasma emission spectroscopy, injection of liquid samples, and of effluent fluids from a chromatographic column, into the plasma space of a source are known. One of the problems before has always been how to get rid of the excess solvent before it hits the plasma region. Conventional flow rates do not allow an excited plasma state to remain in effect. The use of microcolumns in liquid chromatography provides a reduction in solvent flow rate.